U.S. Pat. No. 4,753,890 (=EP 174,343) describes polyesters, such as, for example, polyethylene terephthalate (PET) or polybutylene terephthalate (PBT), which are modified by ethylene-alkyl(meth)acrylate-glycidyl (meth)acrylate copolymers.
U.S. Pat. No. 5,369,154 describes PET/polycarbonate blends containing four different modifiers: a copolymer comprising an epoxide, a copolymer of the core-shell type, an SBR- or SBS- or EPR-type elastomer and a copolymer of the SAN or ABS type. These core-shell copolymers comprise fine particles having an elastomer core and a thermoplastic shell.
Patent EP 115,015 describes PET or PBT containing linear low-density polyethylene (LLDPE), glass fibres and optionally a core-shell copolymer.
Patent EP 133,993 describes PET containing a core-shell copolymer and a copolymer of ethylene with either an alkyl acrylate or (meth)acrylic acid.
Japanese Patent Application JP 01,247,454 A, published on 3 Oct. 1989 describes PBT containing an ethylene-alkyl(meth)acrylate copolymer and an ethylene-glycidyl methacrylate copolymer.
Patents EP 838,501 and EP 511,475 describe compositions similar to those of the above Japanese application.
Patent EP 803,537 describes PET and polycarbonate containing a copolymer comprising glycidyl methacrylate. Firstly, the polycarbonate and the copolymer comprising glycidyl methacrylate are blended together and then this blend is incorporated into the PET.
Patent EP 187,650 describes PET containing a core-shell copolymer and a copolymer of ethylene with either maleic anhydride or a (meth)acrylic acid.
Patent EP 737,715 describes PBTs modified by an impact modifier consisting of an ethylene-methyl methacrylate-glycidyl methacrylate copolymer/core-shell copolymer blend. The amount of impact modifier is from 5 to 20 parts per 100 parts of polyester, i.e. 4.8 to 16.7% for 95.2 to 83.7% of polyester, respectively. The proportions of the glycidyl methacrylate copolymer to the core-shell copolymer are in the ratio 15/85 to 20/80. In the examples, the amount of impact modifier is from 18 parts per 100 parts of polyester, i.e. 15.3%, and the proportion of glycidyl methacrylate copolymer to the core-shell copolymer is in the ratio 3/15, i.e. 17/83.
Patent EP 531,008 describes spent (recycled) PBT/polycarbonate (PC) blends containing core-shell copolymers, to which functionalized copolymers are added in order to make them into a new thermoplastic. These functionalized copolymers are either ethylene-glycidyl methacrylate (GMA) copolymers or ethylene-vinyl acetate-glycidyl methacrylate copolymers. The description quotes proportions of 1 to 97% of polycarbonate, from 1 to 97% of PBT, 1 to 40% of core-shell copolymer and 1 to 40% of glycidyl methacrylate copolymer. In fact, the PBT/polycarbonate blends that it is desired to recycle contain, according to the examples, 15% of core-shell copolymer, which corresponds to more realistic values. Blends (i) of 80 parts of recycled material with 20 parts of glycidyl methacrylate copolymer and blends (ii) of 90 parts of recycled material with 10 parts of glycidyl methacrylate copolymer are then made. The proportions are in the EP 531,008 table below, in which the parts are by weight:
TABLEEP 531 008Compositions such that the core-shell copolymer/PC + PBT ratio =15/85PC + PBT856876.5Core-shell copolymer151213.5(CS)GMA copolymer2010PC + PBT + CS +100100100GMA copolymerGMA/CS copolymer20/12 = (62/38)10/13.5 = (43/57)Proportion of modifier20 + 12 = 32%10 + 13.5 = 23.5%(Core-shell copolymer +GMA copolymer) in PC +PBT
It has been seen from the prior art that saturated polyesters can have their impact properties improved by the addition of a core-shell copolymer. These polymers have a particularly well defined structure in which the core consists of a polymer having an elastomeric character and the shell has a thermoplastic character. It has also been seen that the improvement in impact strength may be obtained by also incorporating a dispersed phase of an impact modifier optionally containing reactive functional groups capable of reacting with the functional groups of the polyesters. This reactivity makes it possible to ensure a fine and homogeneous dispersion of the modifier as well as good adhesion. The core-shell copolymer may itself also be functionalized in order to allow better adhesion to the matrix. However, this reactivity is sometimes high and may lead to a reduction in the melt flow index. This reduction in the melt flow index is prejudicial to the injection moulding of large parts or of fine parts.
It has now been found that it is possible to improve the impact properties of thermoplastic polyesters by adding two kinds of modifier to them, namely (a) a core-shell copolymer and (b) either an ethylene-unsaturated epoxide copolymer or an ethylene-carboxylic acid anhydride copolymer, or a blend of these but in proportions in the polyester and in (b)/(a) ratios which are different from those of the prior art EP 737,715 and EP 531,008. Better impact strength is obtained, while maintaining and even improving the melt flow index.